This invention relates to a waveguide, antenna and vehicular radar apparatus and to, more particularly, a waveguide suitable for microwave or millimeter wave band applications, antenna using the same and vehicular radar apparatus using the same.
In the conventional waveguide structure, a base made of an electrically conductive material has formed therein radio wave input and output ports and a waveguide groove, and a metal plate is intimately attached to a mounting surface on a side in which the waveguide groove is formed, whereby a waveguide is defined between the waveguide groove and the plate. In such the waveguide, in order to prevent any leakage of a high frequency signal through a small gap between the mounting surface of the base and the plate, it is proposed apply a joining by screws, joining by brazing and joining by electrically conductive rubber or electrically conductive bonding agent to ensure a reliable joint between the electrically conductive members to establish an electrical conduction.
However, joining method by screws requires a number of screws tightened with a narrow pitch around the waveguide in order not to allow the metal plate warp and separate from the base due to insufficient tightening force between the screws, so that the manufacturing is not easy. Also, for a small waveguide used in millimeter band or the like, it is not possible to provide a space for securing the screws.
Also, joining method by brazing is poor in productivity and costly and needed a counter measure against over flowed brazing material. The joining by the electrically conductive rubber or the electrically conductive bonding agent has problems in that they generate a loss due to their conductivity lower than metals and also the electrical conductivity is degraded due to aging, rubber protrusion and running of the bonding agent.
It is also proposed, in Japanese Patent Laid-Open Nos. 2004-15579, 2004-221718 and 2000-341030, to combine electrically conductive bumps with a adhesive sheet or a bonding agent, or to use a choking structure provided at the gap to prevent the leakage of a high frequency signal.
However, the combination of the bonding agent and the bump structure has disadvantages of the running of the bonding agent and the breakage of the electrical conduction by the floating of the bumps due to the thermal expansion of the bonding agent. The choke structure is advantageous from the view point of aging, temperature characteristics and manufacture, but needed to have a space for the choking grooves in the vicinity of the gap, so that it is disadvantageous in that the miniaturization is prevented and a very fine choking groove must be provided at a very high cost.
Accordingly, the object of the present invention is to provide a waveguide, antenna and vehicular radar apparatus improved in size, costs, manufacturing and in durability